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This is an image showing a linear string of craters which may have been created when a broken comet such as SL-9 struck the surface.
Click on image for full size NASA/NSSDC and the Space Telescope Science Institute

Craterchains

Observations such as these now suggest that moons of Jupiter have been struck in the past by strings of broken comet material such as that of comet SL-9. The craterchain shown here is found on Jupiter's moon Callisto.

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